When people say "some" and a number, like "some 50,000 people", is there any implication that the number is big or surprising?

Solution 1:

If you look at the dictionary definition of 'some', it seems the word has a variety of meanings and almost behaves as a contronym.

1. an unspecified amount or number of.
   "I made some money running errands"
2. used to refer to someone or something that is unknown or unspecified.
   "I was talking to some journalist the other day"
3. (used with a number) approximately.
   "some thirty different languages are spoken"
4. (pronounced stressing ‘some’) a considerable amount or number of.
   "he went to some trouble"
5. (pronounced stressing ‘some’) at least a small amount or number of.
   "he liked some music but generally wasn't musical"
6. (pronounced stressing ‘some’) expressing admiration of something notable.
   "that was some goal"
   • used ironically to express disapproval or disbelief.
     "Mr Power gave his stock reply. Some help!"

This answer is a bit of a "because the dictionary says so" which is boring - the dictionary only says so because people say so.

You can search the British National Corpus for some _mc* which searches for 'some', followed by a cardinal number, and find that this usage is quite common in a variety of contexts.